Decent explanation of _why_ Facebook came up with the BSD+Patents license: "Facebook’s patent grant is about sharing its code while preserving its ability to defend itself against patent lawsuits."

The difficulty of open sourcing code at Facebook, including React in 2013, was one of the reasons the company’s open-source contributions used to be a fraction of what they are today. It didn’t use to have a strong reputation as an open-source contributor to front-end technologies. Facebook wanted to open source code, though; when it grew communities for projects like React, core contributors emerged to help out and interview candidates often cited React and other Facebook open source as one of the reasons they were interested in applying. People at Facebook wanted to make it easier to open source code and not worry as much about patents. Facebook’s solution was the Facebook BSD+Patents license.